Purifying cast-iron in the manufacture of basic open-hearth steel.



BITE

WILLIAM MUIRHEAD, OF

STATES PATENT FEIQE.

SHETTLESTON, SCOTLAND.

PURIFYI NG CAST-IRON IN THE MANUFACTURE OF BASIC OPEN-HEART STEEL.

Specification of Letters Patent.

Patented July 28,1908.

Application filed April 30, 1908. Serial No. 430,165.

To all whom it may concern:

Be it known that I, WILLIAM MUIRHEAD, iron and steel merchant-and manufacturer, ,2. subject of the King of Great Britain and Ireland, and a resident of Shettleston, Lanarkshire, Scotland, have invented certain new and useful Implrovements in Purifying Castf Iron. in the anufac ture of Basic Open- 1 Hearth Steel ,of which thefollowing is a specihearth or converter steel suitablefor rol ing fication.

My improvements consist of a continuous and connected method and fining or oxidizing the metalloids in ordinary cast iron scrap, cast iron borings and. burned cast iron scrap in open hearth furnaces, and in the production therefrom of basic. 0. en

and other purposes. I My improvements comprise the de-silicpnwing or purifyin of cast iron which can be utilized as a special preparation in the li uid' lpig iron in manu acburned scrap, irres ective of its quality, or

weight. determined by the quantities re uired to be melted and refined. 'lhe-methor of making this de-siliconized or refined liquid cast iron, lends itself to dealing with large, or small qua tities, but the larger the better for the s-ike of economy, and the method. preferred;

is first to put in a charge of cast iron scrap and when this is melted, to make from time It has to time additions of cast iron borings. been'found in actual practice that by my method these additions of cast iron borings, not only melt satisfactorily, but alsov yield up their weight to and amalgamat'e with the liquid charge of cast metal in the melting furnace bath instead of being burned away or oxidized owingto their fine state of divi- S1011. At the same tlme the borlngs or turnings have a refining action whereby the silicon in the original cast iron, ant also the silicon in the borings themselves becomes reduced to within. proper limits from an amount that makes both the original cast iron and the borings unsuitable in their rocess of re- The size 0 the furnace to be used is natural state for making basic open hearth or converter steel, owing to the corrosive action of the silicon in them on the fettling of a basic open hearth furnace or the lining of a converter.

scra or cast iron borin s may be summed up by t e following, name y, metallic iron, carphorus. The percentages of these constituents are approximately:-

Metallic iron. -by difference; 92. 28

' Carbon". 3.25 Silicon'. 2.40 Manganese. 1.00 .07 Phosphorus .1.00

Practically speaking, only the first fourof the six constituents above mentioned are affected in quantity by combustion or oxidation in my process of refining as already described. But. for the should-be sufficient to re er only to the change silicon and carbon. These constituents will be reduced to something like 1.00 per cent. and 2.50 per cent. respectively depending on the with a melting charge of cast iron scrap alone,

heat, but with no further additions, that the silicon and the carbon gradually became reduced to within the required limits, by simle oxidation or combustion. It has been urther l'oundwi/hcn the melting charge conand say about one thirdof cast iron borings,

after it became melted, that the elimination and the recess thereby shortened, than if no bormgs lad been used and that also by s mple oxidation or combustion. The reduction feet and economical manufacture of the steel.

In practice I have found that from 30 to 40 per centum of cast iron borings produces good results; but the percentages will depend on the nature and richness of the bath otcast iron scrap undergoing refining.

As'it is necessary to a proximately determine the percentage of silicon present in the The constituents of ordinary cast ironbon, silicon, manganese, sulfur and phosurpose in view it thafltakes place in the percentages of the that after melting and simply maintaining sisted .of about two-thirds cast iron scrap,-

of the silicon and carbon became expedited,

extent to which the refining might be carried.

In my process of refining it has been found the latter gradually added to the cast iron of silicon so effected facilitates the safe, perbath of metal, spoon samples of the refined metal are taken from time to time from the bath and cast against a cast iron chill block, the percentage of silicon becoming known by the depth of chill of. the sample.

The outstanding advantage of being able to use the old cast iron bormgs, sometimes but rarely called turnings, in the manner I have described is the great economy in cost of'producing this refined and de-siliconized liquid cast iron for its subsequent conversion into basic open hearth or converter steel. The cast iron melting furnace used is preferably acid lined, as the phosphorus is subsequently eliminated in converting the refined liquid cast iron into steel. When the liquid refined metal is at the stage for tapping, it is run, preferably by gravitation, or ladling by mechanical means into an open hearth basic Siemens furnace already heated and char ed with a proportion of steel turnings, (ma leable iron and steel turnings) or ordinary steel scrap, or malleable iron scrap, and these after being brought to a fluid condition and with the necessary additions of limestone, lime,

rolling mill scale, cinder, or other oxids are.

converted into steel in the usual way. Or the de-siliconized cast iron may be conveyed to a converter and made direct into steel.

In a refining melting charge of cast iron scrap or the like, it has been found that a suitable average proportion of the several constituents would be 6 tons of cast iron scrap and 3 tons of cast iron borings, and when burned cast iron scrap is used the charge may consist entirely of this. This charge after refining is in its liquid state transferred as previously described into an open hearth basic steel melting furnace,

which has already been charged with from' say 9 to 191 tons of iron or steel turnings or other malleable scrap and reduced to a fluid condition and the Whole charge converted into steel in an ordinary manner.

in my process practically speaking, by the term desiliconizing meant the elimination by oxidation or combustion, as described in the body of the specification, of say to 75 per centum of the silicon from ordinary cast eeepm iron scrap, cast iron borings, or burned cast iron scrap which usually contain say about 2 to 3 per centum of the element silicon Whereb it becomes reduced to a limit of somethingl li e .5 to 1 per centum in my liquid refine cast iron. Of course the percentage of silicon maybe lowered or raised in the refined liquid cast iron beyond these limits by my process if so required, for subsequent conversion into basic open hearth or converter steel. What I claim as my invention and desire to secure by Letters Patent is 1. A process of making steel which consists in melting a charge of cast iron scrap in an open hearth furnace, adding cast iron borings gradually to the molten charge in suitable proportion up to 40% of the original charge to expedite the removal of the silicon present, and converting the refined metal so produced into steel, substantially as described.

2. A process of making steel which consists in melting a charge of cast iron scrap in an open hearth acid lined furnace, adding cast iron borings gradually to the molten charge in suitable proportion up to 40% of the original charge to expedite the removal of the silicon present, and converting the refined metal so produced into steel, substantially as described.

3. A process of making steel which consists in melting a charge of cast iron scra in an open hearth furnace, adding cast iron orings gradually to the molten charge in suit able proportion up to 40% of the original charge to expedite the removal of the silicon present, leading the molten metal so refined to a basic open hearth furnace. previously heated and charged withmalleablc scrap, and converting the combined charge into steel, substantially as described.

In testimon whereof I-havc si ned in name to this specification, in the presence of two subscribing witnesses.

Wlvl'. MUI lil I PM D.

Witnesses R. C. THOMSON, THOMAS E. BROWNLIE. 

